I don't know why commenters are getting on the MC's case at this point, especially when you have the whole premise in Chapter 1. If you're still following after 22 chapters, then it makes no sense to complain.
Sayu is a runaway who's been sexually abused and taken advantage of, and states this at the beginning of the story. Of course the author was going to bring the source of the trauma full circle and introduce a character that would trigger those experiences.
But then readers are upset when the MC takes the abuser out of the house without either a verbal 'victory' or physical altercation? Why would that have solved anything? Throwing the MC into further legal trouble? The point of the story is to show how two emotionally unstable characters look to each other for some source of comfort/validation. The MC couldn't argue the abuser's arguments because he knows he's also in the wrong for harboring a runaway minor. The abuser, who has far more to answer for, goes out looking smug because he doesn't have any remorse for his actions. Meanwhile the MC, with a conscience, is facing an internal struggle.
Edit: The abuser's actions are obviously not equal to the MC's, but unlike the abuser, the MC cares. That's why the abuser 'wins' the argument, because he doesn't have any qualms about the situation
I think this story is interesting in concept and execution, which is why I'm following it. I'm not looking for role models in any of the main characters, because that's not the story's intent. I have some gripes with it, but this current story thread seems perfectly in line with what has happened in the past 22 chapters.